A multimedia decoder unit having error concealment and fast muting capabilities. The audio decoder provides error concealment using a dynamic recovery delay that is based on the error rate of an input digital bitstream and also uses frame repeating. The decoder allows fast audio muting whereby audio can be muted within two audio frames of a mute signal that immediately freezes the video frame, e.g., a channel change. With respect to the dynamic recovery delay, a template of fixed length is used to inspect the last frames within the template. If error is found, then the error sum is used as an index into a table length which provides a dynamic template length. Error within the dynamic template length is computed and if larger than a tolerance, the current frame is muted. This allows the recovery delay to be adaptive and based on the error rate while still allowing mute merging. Muting the current frame can be achieved by repeating the previous frame but the delay data of the last block of the previous audio frame is added to the first block of the repeated audio frame to provide a smooth frame interface. In response to a mute command, the decoder zeros the audio output bitstream stream to provide zero frames at the audio output buffer (AOB). In addition, the decoder also directly zeros audio frames in the AOB that lie between its the read and write pointers to guarantee that only two frames of audio be played after the mute signal.
Legal claims defining the scope of protection, as filed with the USPTO.
1. In a digital decoder unit, a method for reducing audio frame over-run comprising the steps of: a) receiving an audio encoded bitstream, decoding said encoded bitstream and storing decoded audio frames into an audio output buffer; b) responsive to an audio mute signal, causing an audio bitstream of said decoder unit to zero, said step b) causing entries in said audio output buffer to zero starting from an entry position pointed to by a write pointer associated with said audio output buffer; and c) directly zeroing a plurality of entries of said audio output buffer in response to said audio mute signal, said plurality of entries being a few entries away from a read pointer of said audio output buffer, said read pointer following said write pointer and wherein as a result of step b) and step c), only a predetermined number of audio output frames are guaranteed to be played after said audio mute signal is detected.
2. A method as described in claim 1 further comprising the step of d) freezing a current video frame on a display screen in response to said audio mute signal being detected and wherein said audio mute signal is generated as a result of a channel change command.
3. A method as described in claim 1 wherein said read pointer and said write pointer are separated by a predetermined number of entries and wherein said audio output buffer is a circular buffer.
4. A method as described in claim 3 wherein said predetermined number of entries is four and wherein said predetermined number of audio output frames is two.
5. A method as described in claim 1 wherein said encoded bitstream is substantially compliant with the AC3 digital audio standard.
6. A method as described in claim 1 wherein step c) is performed using a windowing function.
7. In a digital decoder unit, a method for reducing audio frame over-run comprising the steps of: receiving an audio mute signal; zeroing an audio bitstream of said decoder in response to said audio mute signal; and zeroing entries in an audio output buffer starting from an entry position pointed to by a write pointer associated with said audio output buffer said entries being away from a read pointer of said audio output buffer, said read pointer following said write pointer and wherein only a predetermined number of audio output frames are guaranteed to be played after said audio mute signal is received.
8. A method as described in claim 7 wherein said read pointer and said write pointer are separated by a predetermined number of entries and wherein said audio output buffer is a circular buffer.
9. A method as described in claim 7 further comprising the step of: freezing a current video frame on a display screen in response to receiving said audio mute signal, wherein said audio mute signal is generated as a result of a channel change command.
10. A method as described in claim 8 wherein said predetermined number of entries is four and wherein said predetermined number of audio output frames is two.
11. A method as described in claim 7 wherein said audio bitstream is encoded and is substantially compliant with the AC3 digital audio standard.
12. A method as described in claim 7 wherein a windowing function guarantees said predetermined number of audio output frames.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
May 4, 2004
August 26, 2008
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